What event made Equiano most afraid of the traders?

From the text:

The first object which saluted my eyes when I arrived on the coast was the sea, and a slave ship, which was then riding at anchor, and waiting for its cargo. These filled me with astonishment, which was soon converted into terror when I was carried on board. I was immediately handled and tossed up to see if I were sound by some of the crew; and I was now persuaded that I had gotten into a world of bad spirits, and that they were going to kill me.